Effects of fertilization on drought responses in saplings of three European trees species

Nutrient and water supply are decisive limiting factors for trees and their productivity. Yet, the consequences of fertilization for drought responses, especially during the sensitive nursery stage, remain poorly understood. In this study, we exposed potted saplings of Pinus sylvestris L., Fagus sylvatica L. and Quercus robur L. to two levels of fertilization and three water regimes. The effects of fertilization, drought and their interaction on gas exchange, hydraulic traits and growth were examined. Fertilization generally promoted gas exchange, hydraulic conductance and biomass accumulation but responses were species-specific and did not always persist under and after drought. While fertilized Q. robur maintained or even increased its biomass and physiological performance under drought, the benefits of fertilization for P. sylvestris and F. sylvatica diminished under increasing drought intensity. No consistent changes in drought resistance traits (e.g., turgor loss point, embolism resistance) were observed across species in response to fertilization, which may indicate limited plasticity or acclimation potential of saplings. Our findings highlight the species-specific fertilization effects on drought responses and post-drought performance of saplings, emphasizing the need to consider both factors in silvicultural practices under future climate scenarios.